Project Summary/Abstract Heart failure (HF) is a major public health problem worldwide, and half of patients presenting with HF have preserved (HFpEF), rather than reduced ejection fraction. However, HFpEF remains a therapeutic challenge, given current limited understanding of causal and contributing factors, and clinical heterogeneity within HFpEF subphenotypes. Comorbidities such as obesity and hypertension are thought to induce a systemic pro- inflammatory state that, in turn, drives cardiovascular dysfunction and remodeling leading to HFpEF. Indeed, downstream markers of inflammation have been observed in HFpEF. However, accumulating evidence suggests that upstream mediators of inflammation are more likely to play a causal role in disease pathogenesis and, in turn, serve as effective therapeutic targets. Upstream initiation of inflammation in humans is governed primarily by small molecule effectors of arachidonic acid metabolism, termed eicosanoids. These bioactive lipids include thromboxanes, prostaglandins, lipoxins, and leukotrienes, and harbor pro- and anti-inflammatory activity, vasoactivity, and direct modulation of cardiomyocyte signaling and contractile function. To date, the interaction between eicosanoid pathways and development of HFpEF remain poorly understood, thus limiting our ability to harness their therapeutic potential. Advanced methods using mass spectrometry now allow for the rapid and accurate quantification of >150 upstream eicosanoid mediators representing multiple enzymatic origins. To provide a more detailed understanding of how upstream eicosanoid pathways may underlie the progression from risk factors to HFpEF, and shed light onto HFpEF subphenotypes, we will pursue two related lines of investigation: In Aim 1, we will investigate the association of circulating eicosanoids with clinical risk factors, subclinical cardiac remodeling, and incident HFpEF in the community. In Aim 2, we will examine the association of eicosanoid profiles with HFpEF subphenotypes, including distinct cardiac and extracardiac vascular dysfunction among clinical HFpEF patients. This proposal leverages a unique multidisciplinary team of collaborators with expertise in clinical epidemiology, advanced imaging, exercise physiology, bioinformatics, analytical chemistry, and lipidomics. Our systematic approach to comprehensively investigating the components of upstream inflammatory activity in two large, well-phenotyped community-based cohorts, complemented by a group of clinical HFpEF patients with comprehensive exercise hemodynamic evaluations and deep physiologic phenotyping to assess distinct aspects of cardiovascular dysfunction, promises to yield important insights into the molecular determinants of HFpEF. Importantly, these studies will lay the foundation for future investigations focused on disease prevention and optimal therapies tailored to HFpEF subphenotype.